1. The Field of the Invention
The present invention relates to orthodontic brackets, more particularly to self-ligating orthodontic brackets that include a bracket base, at least one slot or other feature for receiving an arch wire, and a ligation cover.
2. The Relevant Technology
Orthodontics is a specialized field of dentistry that involves the application of mechanical forces to urge poorly positioned, or crooked, teeth into correct alignment and orientation. Orthodontic procedures can be used for cosmetic enhancement of teeth, as well as medically necessary movement of teeth to correct underbites or overbites (“buck teeth”). Orthodontic treatment can improve the patient's occlusion, or enhanced spatial matching of corresponding teeth.
The most common form of orthodontic treatment involves the use of orthodontic brackets and wires, which together are commonly referred to as “braces”. Orthodontic brackets, more particularly the bracket bases, are small slotted bodies configured for direct attachment to the front (or “labial”) surfaces of the patient's anterior, cuspid, and bicuspid teeth or, alternatively, for attachment to bands which are, in turn, cemented or otherwise secured around the teeth. Once the brackets are affixed to the patient's teeth, such as by means of glue or cement, a curved arch wire is inserted into the slot of each bracket. The arch wire acts as a template or track to guide movement of the teeth into proper alignment. End sections of the arch wire are typically captured within tiny appliances known as “buccal tubes” affixed to the patient's molars.
There are two distinct classes of orthodontic brackets: those that require the use of ligatures to fasten the arch wire to the bracket, and those that are self-ligating. Before the emergence of self-ligating brackets, small ligature wires or elastomeric bands were necessary to hold the arch wire in a securely seated position in the brackets. Ligatures or some other form of fastening means are essential to ensure that the tensioned arch wire is properly positioned around the dental arch, and to prevent the wire from being dislodged from the bracket slots during chewing of food, brushing of teeth, or application of other forces. One type of commercially available ligature is a small, elastomeric O-ring, which is installed by stretching the O-ring around small wings known as “tie wings” that are connected to the bracket body. Metal ligatures may also be used to retain arch wires within the bracket slots.
In an effort to simplify the process of installing braces, various self-ligating brackets have been developed. The term “self-ligating bracket” refers to a class of orthodontic brackets that include some sort of ligation cover or clasp which encloses or otherwise retains the arch wire within the slot of the base. There are both “passive” and “active” self-ligating orthodontic brackets. The term “passive” bracket refers to brackets that only loosely retain the arch wire therein, such that considerable movement between the arch wire and bracket base is possible. The term “active” bracket refers to brackets in which the self-ligating arch wire cover exerts force onto the arch wire, resulting in more precise and controlled tooth movement.
The first self-ligating bracket, known as the Russell bracket, was developed by Dr. Jacob Stolzenberg in the early 1930s. This bracket, which uses a set screw to ligate the arch wire within a slot of a threaded base, was revolutionary but perhaps ahead of its time because the concept of self-ligating brackets fell more or less into obscurity until the early 1970s.
In 1971, Dr. Jim Wildman of Eugene, Oreg. developed the EDGELOK bracket, which has a round body with a rigid labial sliding cap. A special opening tool is used to move the slide occlusally for arch wire insertion. When the cap is closed over the arch wire with finger pressure, the bracket slot is converted to a tube. The EDGELOK bracket was the first “passive” self-ligating bracket. That is, the bracket, while retaining the arch wire therein, does not exert pressure onto the wire. Instead, the arch wire is free to slide relative to the bracket. The EDGELOK bracket is described in U.S. Pat. Nos. 3,748,740 and 3,854,207 to Wildman. Other patents to Dr. Wildman include U.S. Pat. Nos. 5,094,614, 5,474,446 and 5,863,199. In 1998, Dr. Wildman introduced the TWIN-LOCK bracket, which includes a flat, rectangular slide, housed between the tie wings of an edgewise twin bracket.
A similar bracket to the EDGELOK bracket, called the MOBIL-LOCK bracket, was developed by Dr. Franz Sander of Ulm, Germany, which requires a special tool to rotate the semicircular labial disk into the open or closed position.
Between 1976 and 1980, Dr. Herbert Hanson of Hamilton, Ontario, Canada developed the SPEED bracket, which features a curved spring clip that wraps occluso-gingivally around a miniaturized bracket body. The clip is moved occlusally using special tools to permit arch wire placement, then seated gingivally using finger pressure. The clip constrains and interacts with the arch wire to some degree such that the SPEED bracket was the first “active” bracket system.
In 1986, Dr. Erwin Pletcher developed the ACTIVA bracket, which has an inflexible, curved arm that rotates occluso-gingivally around a cylindrical bracket body (see U.S. Pat. Nos. 4,077,126, 4,371,337, 4,419,078, 4,522,490, 4,559,012 and 5,322,435 to Pletcher). The arm can be opened and closed using finger pressure.
In 1995, Dr. Wolfgang Heiser of Innsbruck, Austria developed the TIME bracket, which is similar in appearance to the SPEED bracket, and which features a rigid, curved arm that wraps occluso-gingivally around the labial aspect of the bracket body. A special instrument is used to pivot the arm either gingivally into the slot-open position, or occlusally into the slot-closed position. The stiffness of the bracket arm prevents any substantial interaction with the arch wire, thereby making the TIME bracket a passive bracket.
Dr. Dwight Damon of Spokane, Wash. developed the Damon SL I and the Damon SL II brackets in 1996 and 1999, respectively (see U.S. Pat. No. 6,071,118 to Damon). Both are edgewise twin brackets. The difference between the two is that the first features a labial cover that straddled the tie wings, while the second incorporates a flat, rectangular slide between the tie wings. In both versions, the slide moves incisally on the maxillary brackets and gingivally on the mandibular brackets. Special opening and closing pliers are required to move the slide.
There are many other variations and adaptations of the foregoing self-ligating brackets that have been developed by others. See, e.g., U.S. Pat. No. 4,786,252 to Fujita, U.S. Pat. No. 4,712,999 to Rosenberg, U.S. Pat. No. 4,492,573 to Hanson, U.S. Pat. No. 4,103,423 to Kessel, and U.S. Pat. No. 6,071,119 to Christoff et al.
In general, conventional self-ligating brackets are complicated in design, complex to assemble, and difficult to use in practice. Conventional orthodontic brackets often require many trips to the orthodontist for periodic readjustment and maintenance. Therefore, there has been a long-felt need to find new designs and materials that can simplify the manufacture of orthodontic brackets, as well as the installation and subsequent maintenance of such brackets. In particular, there is a need for orthodontic brackets that are easy to open and close, that provide active ligation without the need for special tools to open and close the arch wire restraining means, which are easily manufactured and installed by the orthodontist, which provide greater versatility together, and which are of simplified design.
For example, it would be an improvement in the art to provide one-piece, self-ligating orthodontic brackets that can be manufactured in a single molding step. It would be a further improvement to provide self-ligating brackets that include a plurality of plastic materials from which the base and cover can be made so as to maximize the beneficial properties of each plastic material. It would be an additional improvement to provide orthodontic brackets with special hinge and locking features between the ligation cover and bracket base or increased safety and ease of use. It would be an improvement to provide orthodontic brackets capable of dynamic active ligation of an arch wire as the tooth is realigned so as to reduce or eliminate the need for subsequent adjustments. It would yet be an improvement to provide orthodontic brackets having two or more initially open arch wire slots that can be ligated by a single ligation cover. It would also be an improvement to provide a ligation cover that was biased so as to preferentially remain in an open and/or closed position.
Orthodontic brackets that incorporate one or more of these and other improvements are disclosed and claimed herein.